BEE Electro cap question

[Govmnt_Lacky]

Question about electro cap function:

If I connect an electro cap to DC voltage on the positive side, say 16VDC and I leave the negative side floating... should I be reading a DC voltage on the negative side when measured to GND? Does the negative side have to be tied to a potential in order for the cap to block the DC?

Thanks!

[anotherjim]

The negative end of the cap will read to the + supply but drop to 0v as the cap charges via the meter load impedance. A fully discharged cap will "look" like a short circuit. When you remove the meter the cap will remain charged until discharges via leakage.
Is this actually a question about coupling caps disconnected by a switch? A cap only blocks current flow from DC when the DC volts across the plates is stable. A signal isn't stable so that passes.

[Govmnt_Lacky]

The negative end of the cap will read to the + supply but drop to 0v as the cap charges via the meter load impedance. A fully discharged cap will "look" like a short circuit. When you remove the meter the cap will remain charged until discharges via leakage.
Is this actually a question about coupling caps disconnected by a switch? A cap only blocks current flow from DC when the DC volts across the plates is stable. A signal isn't stable so that passes.

Doing a bit of troubleshooting at my work.

Essentially, I have an in-line microphone amplifier that requires DC to power it. The DC rides on the same line as the voice. I need the electro cap to filter the DC voltage prior to arriving at the radio input BUT, allow the A/C "voice" signal to pass. When I disconnect the radio input, I am still seeing DC voltage on the input line. I am "assuming" that when the radio input is connected, it will complete the circuit and the electro cap will filter properly.

[anotherjim]

You'd be right to see a voltage out of the blocking cap, but it shouldn't be much for long. It depends on the impedance of whatever you measure it with. A theoretical infinite impedance meter would always read the DC supply volts "through" the cap.
Mind you, if the cap was itself leaky, it would look like a resistor of some value. So if the voltage doesn't sag to zero in a reasonable amount of time, maybe it's a bad cap?

Since electro caps are usually a little leaky and if the meter impedance is high (10M or >) then you have a voltage divider with the leakage resistance and then the cap negative will never charge to 0v via the meter and you read some voltage!

You have to find the meter impedance, match that with the minimum volts on the blocked side of the line and judge if that amounts to acceptable leakage or to replace that cap.

[Govmnt_Lacky]

You'd be right to see a voltage out of the blocking cap, but it shouldn't be much for long. It depends on the impedance of whatever you measure it with. A theoretical infinite impedance meter would always read the DC supply volts "through" the cap.

I am seeing the DC voltage slowly dissipate when taking the readings. I am using a Fluke meter.

[anotherjim]

That's probably ok then. Fluke is 20Meg input?

[antonis]

If I connect an electro cap to DC voltage on the positive side, say 16VDC and I leave the negative side floating...

You DON'T connect that cap to any voltage..!!

P.S.
"Voltage" is considered the potential difference between two distinct points..
(here you have only one point connected somewhere - the exact connection place is totally aloof both for cap and voltage source..)